The conventional modern method of relaying switches comprises the steps of locating hydraulic lifting mechanisms over the old switch, raising the old switch, assembling and locating a temporary track in the place of the old switch, moving small trolleys on to the temporary track, lowering the old switch on to the trolleys and removing the old switch and the lifting mechanisms; followed by location of the new switch on the trolleys, relocating the lifting mechanisms (used for raising the new switch on to the trolleys), rolling in the trolleys with the new switch, raising the switch by the lifting mechanisms, removing the temporary track, lowering the new switch into position and then finally moving the lifting mechanisms.
Several disadvantages have been experienced with this method. For example, the hydraulic lifting mechanisms are required to lift very large loads and also to provide a "walking" function in order to load the new switch from a location near or adjacent the site of the old switch on to the trolleys, and also to provide adjustment of the exact location of the new switch in its final position. This latter adjustment of location has caused considerable problems and often results in a man-handling operation since the degree of adjustment is rather limited.
Another disadvantage of the conventional method is that of the necessity to remove the lifting mechanisms so that the ballast can be treated or replaced prior to laying of the new switch.
Yet another difficulty or inconvenience of the conventional method was that the new switch had to be assembled at the site or near the site of the old switch, although it has been proposed to move switches from a central manufacturing location in the vertical condition on a truck which was low enough for the upper extremity of the switch not to foul overhead lines, tunnel roofs and the like. With existing apparatus, an additional step had to be performed, namely the turning of the switch from the vertical to the horizontal position prior to location.
A search in the European Patent Office revealed the following patents:
French Pat. No. 2 325 765 (Drouard) which shows an arrangement in which a car carries a new panel and has means to support the panel in a vertical or horizontal position. The old and the new panels are conveyed on the same car.
French Pat. No. 41 694 (Collet) relates to a hoist or carrier for the old and new panels which are carried on a small carrier.
German Pat. No. 2 432 326 (Seidler) teaches the use of hoists with a series of "walkers", as described above.
French Pat. No. 2 314 299 (Profimex) requires more than two lifters and requires "walkers" as well.
U.S. Pat. No. 3 425 359 (Kawamura) also makes use of "walkers".